Started at about 8 degrees the other day without using grid heater or block heater. After two long sets of three cycles of the plugs it finally took. That's with the 7v's. I tried a two cycle set and no good. I wait a full five seconds each cycle. Better upgrade that plastic bit in your ignition switch if you're going to cycle it like this

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05 CRD: H.D.S2 stat,WW Ironrock trilink&LCA's, OX rear,ARB front, 4.10's, ARB bumper, Suncoast,OME 3.5, JBA UCA,rock rails, Moabs&265/75 Duratracs, GDE tunes ,FFD fan,ARP's, 2 micron fuel, new valves,sasquatch battery tray & grid heater, tensioner relocated
Mech fan, VH & AC delete